1. Field of the Invention
The present invention relates to a method for manufacturing a graphene film and a graphene channel of transistor. More particularly, it relates to a method for manufacturing a graphene film and a graphene channel of transistor under low temperature.
2. Description of Related Art
Graphene is famous for the most fantastic material in this century, in which is formed by carbon atoms in a single layer. In this material, carbon atoms are densely arranged in a regular hexagonal pattern by sp2 hybrid orbital, and the lattice arrangement in honeycombs shape extends to form a planar two-dimensional material. Furthermore, graphene is a one-atom-thick planar sheet, and it is the thinnest and strongest nanomaterial in the world.
Many different approaches have been developed for manufacturing graphene, such as mechanical exfoliation, SiC sublimation, and chemical vapor deposition (CVD). For the mechanical exfoliation method, only flakes of graphene are obtained. For the SiC sublimation method, the high price of the SiC substrates is the major concern for practical applications. Accordingly, those applications in the industry are limited a lot.
Therefore, the CVD technique has become a common approach to obtain graphene films. This method has exhibited advantages like large-area graphene growth and controllable layer numbers. In CVD method, Ni and Cu are two metals commonly used as the substrates. Different from the growth mechanisms comprising C atom dissolution and precipitation by using a Ni template, the low solubility of C atoms in Cu foil results in different graphene growth mechanisms, comprising surface migration and self-align arranged construction of C atoms on the Cu foil. Therefore, uniform single-layer graphene films can be obtained by using Cu substrates. The required graphene growth temperature depends on the temperature needed for cracking the hydrocarbon source to supply the C atoms. By using the common precursor methane, the growth temperature is usually around 1000° C. To decrease the growth temperature, different approaches have been investigated by using different precursors. By using other gases, such as hexane, methanol or ethanol, graphene films can be obtained at a decreased growth temperature ranged from 950 to 650° C. The lowest growth temperature reported in literatures is 300° C. by using benzene as the carbon source in a low-pressure CVD chamber. However, in that report, only graphene flakes are obtained. On the other hand, the growth temperature for Ni substrate is usually kept at 900-1000° C. due to the required carbon dissolution procedure.
For the conventional technologies, the graphene film transferring and reattachment procedures are required for both Ni and Cu substrates after growth. In this case, it seems that the high-temperature growth procedure may not influence the following device fabrication. However, the graphene transferring procedure does not fit in the standard fabrication procedures for semiconductor devices, which limits the potential applications of this material. In order to solve the problem of graphene transferring procedure, references have reported direct growth of graphene on a silicon dioxide substrate by evaporating copper on the silicon dioxide substrate and using methane as a carbon source, and this mechanism is the same as the mechanism of CVD method. Carbon atoms aggregate to form a graphene film between the metal and silicon dioxide substrate after annealing at a high temperature. These growth mechanisms are mainly identical with the CVD method, so the process keeps at a high temperature. On the basis of the above-mentioned references, direct growth of graphene at a lower temperature would be the important first step to integrate graphene growth into semiconductor fabrication lines. Thus, the present invention provides a method for manufacturing graphene by using molecule beam epitaxy (MBE) at a low temperature, such that the characteristics of the obtained graphene and that of the existing graphene are identical in order to meet long-felt need in the industry.